1. Field of the Invention
The present invention relates to a toner for use in electrophotography, in image-forming methods for developing an electrostatic image, and in toner jets.
2. Description of the Related Art
The demands for higher image quality, higher speeds, and greater energy conservation have become increasingly severe in recent years in the field of image-forming devices such as copiers and printers. In addition, the use environment has also become more diverse, and excellent properties must now be maintained even in high-temperature, high-humidity environments and low-temperature, low-humidity environments. More specifically, there is a demand that high-quality images be obtained even after image formation has been carried out over a large number of prints, i.e., that an excellent endurance stability be exhibited.
On the other hand, reducing the fixation temperature of the toner is known to be effective for achieving energy conservation in, for example, copiers. Various proposals have thus already been made with the goal of improving the low-temperature fixability of toners.
For example, Japanese Patent No. 4,898,384 proposes a blend of binder resins with different softening points using polyester/styrene-acrylic hybrid resins as the binder resins.
This makes it possible to achieve a good balance between the low-temperature fixability and the endurance stability by improving the low-temperature fixability using a low softening point component while maintaining the endurance stability using a high softening point component.
However, various problems occur when the attempt is made to satisfy additional demands on the low-temperature fixability using the art of blending binder resins that have different softening points. For example, when the softening point is lowered in order to achieve the low-temperature fixability, the endurance stability may decline in high-temperature, high-humidity environments and the density may then decline with an increasing number of prints. In addition, depending on the binder resins being blended, the dispersibility of the release agent (wax) has declined and as a result fogging has been produced in low-temperature, low-humidity environments. To counter this, the chemical bonding of an aliphatic compound to the binder resin has been proposed with the goal of improving the low-temperature fixability and the wax dispersibility.
For example, in order to improve the wax dispersibility, a method in which stearic acid (70° C.) is condensed with the binder resin is proposed in Japanese Patent No. 4,116,534.
In order to improve the low-temperature fixability, a method in which a C10-24 aliphatic compound is condensed is proposed in Japanese Patent No. 4,402,023.
Aliphatic compounds, because they have a near-wax structure, do provide an improvement in the wax dispersibility when condensed with the binder resin. Moreover, some plasticization of the binder resin is also thought to occur when a low melting point aliphatic compound is condensed with the binder resin, and it is known that the low-temperature fixability is improved by introduction into the binder resin.
However, the density of the obtained image has undergone a decline during extended use in high-temperature, high-humidity environments. High melting point aliphatic compounds, on the other hand, have a low plasticizing effect, and it has thus been quite difficult to obtain the required low-temperature fixability with them.
Thus, additional improvements are essential for achieving the even better low-temperature fixability, endurance stability, and wax dispersibility that are required by electrophotography.